Manganese(I)-Catalyzed C-H Activation: The Key Role of a 7-Membered Manganacycle in H-Transfer and Reductive Elimination.

Manganese-catalyzed C-H bond activation chemistry is emerging as a powerful and complementary method for molecular functionalization. A highly reactive seven-membered Mn(I) intermediate is detected and characterized that is effective for H-transfer or reductive elimination to deliver alkenylated or pyridinium products, respectively. The two pathways are determined at Mn(I) by judicious choice of an electron-deficient 2-pyrone substrate containing a 2-pyridyl directing group, which undergoes regioselective C-H bond activation, serving as a valuable system for probing the mechanistic features of Mn C-H bond activation chemistry.